1. Field of the Invention
This invention relates to a combustion chamber configuration for a reciprocating piston, direct injected diesel cycle internal combustion engine.
2. Related Art
A piston arrangement for achieving improved control over ignition and combustion characteristics of a fuel charge in an internal combustion engine and a process for achieving such controlled ignition and combustion by the generation and management of fuel radical species within the combustion chamber of such an engine is described in U.S. Pat. No. 4,898,135 granted Feb. 6, 1990. In accordance with the patent, a piston for an internal combustion engine, which may be spark or compression ignited, includes a central recess for receiving the majority of each charge during each combustion cycle of the engine, and a reaction chamber adjacent the recess for receiving a portion of the fuel and air of each charge. During each combustion cycle, the portion of the charge that is disposed in the reaction chamber undergoes a cool flame oxidation reaction to produce fuel radicals and intermediate species that are discharged in a next succeeding combustion cycle for seeding the next charge admitted to the combustion chamber.
In accordance with the teachings of the aforesaid patent, the generation and management of fuel radicals requires control over the manner in which the fuel and air of each charge is admitted into the reaction chamber and also the manner in which outgasing of the reaction chamber into the combustion zone occurs. In accordance with U.S. Pat. No. 4,898,135, a continuous slot orifice having critical dimensions is provided to primarily receive fuel and air into the reaction chamber under choked flow conditions during the compression event of each combustion cycle and to enable outgasing of the chamber into the main combustion chamber also under choked flow conditions, whereby a supply of fuel radical species is preserved during each combustion cycle for use in the next combustion cycle due to the time delay in outgasing of the reaction chamber. Optionally, in accordance with the teachings of the prior U.S. Pat. No. 4,898,135, one or more discrete orifices may also be provided to provide communication between the piston recess and the reaction chamber to achieve better control over the admission of fuel to the reaction chamber.
For a complete discussion of the benefits provided by the piston configuration described above, and for a more complete explanation of the manner in which fuel radical species are generated and managed in accordance with a piston having a configuration as described above, reference may be had to the written description and drawings of the U.S. Pat. 4,898,135. Essentially, the patent describes the manner in which controlled seeding of a fuel charge before ignition in an internal combustion engine can be utilized to produce dependable and predictable ignition and knock-free combustion of fuels that otherwise would be considered difficult to ignite without ignition improvers or subject to knock during certain engine operating conditions, depending upon the type of engine utilized. The generation and management of the supply of radicals in the combustion chamber to achieve the recognized benefits of seeding a fuel charge with such radicals involves using a reaction chamber located adjacent a piston recess with a system that provides controlled communication between the main combustion chamber of the engine and the reaction chamber.
In an improvement over the system and process described in U.S. Pat. No. 4,898,135, the continuous slot orifice was eliminated in favor of at least one discrete orifice intended to primarily control admission of the fuel portion of each charge into the reaction chamber and at least one separate discrete orifice located separately from the first discrete orifice and arranged to control admission of primarily air into the reaction chamber. This improvement is described in U.S. Pat. No. 5,322,042 granted Jun. 21, 1994.
Essentially, in accordance with U.S. Pat. No. 5,322,042 the axially extending sidewall of the piston recess similar to that described in U.S. Pat. No. 4,898,135 is provided with at least one discrete orifice that is intended to control admission primarily of fuel into the reaction chamber during each combustion cycle, and at least one separate, physically separated discrete orifice is provided to control admission primarily of air into the reaction chamber. By configuring the orifices and adjusting their location to optimize the fluid circulation and heat transfer conditions within the reaction chamber, optimization of the generation of fuel radical species is achieved. Likewise, outgasing of the radical species into the main combustion chamber during a succeeding combustion cycle (i.e., during the intake event) is also achieved in a more controlled manner, since the location of the orifices will contribute to the injection of the radical species into the main combustion zone.
It has been discovered more recently that reduction of soot (mostly carbon containing particles resulting from partial combustion of fuel) produced during combustion in such combustion chambers in a diesel cycle engine can be markedly achieved if one or more orifices in communication with the reaction chamber are located along the axial wall defining the piston recess so as to effect discharge of radical species from the reaction chamber into a soot cloud in the recess that is formed during the combustion portion of each combustion cycle.